As part of the 3GPP 5G study a base station architecture was proposed in which the base station includes a Central Unit (CU) and Distributed Units (DU).
The traditional protocol layers are split between CU and DU.
One of the drawbacks of this solution is that packets might be lost on the CU-DU interface without the possibility to identify the packets lost over the transport network, retransmit them and eventually increase the reliability of the communication over the transport network.